Britney Spears turned up the heat as she and a scantily clad Rihanna staged a mock pillow fight at a top US awards night.

Britney joined Rihanna as she performed her hit S & M at the Billboard Music Awards, which were held in Las Vegas.

Rihanna and Taylor Swift were key winners at the event, which featured Beyonce, U2, the Black Eyed Peas – and even First Lady Michelle Obama.

The show, which was packed with performances saw Rihanna named radio artist of the year and top female artist.

Swift won top album artist for the multimillion-selling Speak Now. She also won top country artist.

Beyonce, received her special Millennium Award for her career achievements from her mother Tina Knowles and was lauded in a video by legends and luminaries, including Stevie Wonder, Barbra Streisand and Mrs Obama.

The 29-year-old said: "This is a moment I have to soak in because it's gonna be – and it is – one of the best moments of my life."

And Diamond, who received Billboard' "Icon" award, said: "I would have settled for a top 10 record."

U2 were top touring act and Black Eyed Peas won best duo or group.